| Objective: Percutaneous laser disc decompression (PLDD) has beenproved to be an mature, safe and effective treatment for cervical or lumbar disc herniation recently. The basic principle is as follows, When the needle is in place, its correct position is verified by using biplanar fluoroscopy, sometimes in combination with CT imaging. A laser fiber isinserted through the needle into the center of the nucleus pulposus. Laser energy is then delivered into the nucleus pulposus to vaporize its content and reduce intradiskal pressure. Thus, we can reduce the mechanical pressure of adjacent nerve root caused by the extrusive of the disc,and to mitigate or eliminate radicular symptoms. However, there is no uniform report about laser parameters for this kind of minimally invasive treatment refer to the extensive lieratures, such as output power and totalenergy. Coupled with the lack of experimental study about these basicresearch work for PLDD, little is known about the effect of thermal conductivity in intervertebral disc induced by1064nm Nd:YAG laser irradiation with different parameters at present. The current situation is not conducive to the replication and exchange of successful experience for PLDD, which also caused a great potential risk of thermal damage to theintervertebral disc tissue and adjacent cartilage endplates. The aim of this paper is to study the thermal conductivity on lumbar disc nucleus pulposus by Nd:YAG laser irradiation with different parameters, and investigate the risk of thermal damage to adjacent cartilage endplates duringlaser decompression surgery.Methods: Thirty-two experimental specimens manufactured with goat spines were divided into four groups randomly according to laser pow er(n=8), and all experimental specimens were irradiated with a Nd:YAGlaser (λ=1064nm) at0w,5w,10w and20w. The irradiation was underroom temperature (20°C) condition with pulses of1s and pauses of1s,and stopped when delivering a total energy of800J. A three-point temperature change at a distance of5mm(A) in front and2mm(B),5mm(C)in side of the optical fiber tip were monitored by multi-channel thermometer.The postoperative experimental specimens were placed in the refrigerator at-20℃immediately for24hours, and then taken for histologicalexamination.Results:Compare the temperature of the three-point measured at100J,200J,300J,400J,500J,600J,700J,800J respectively:Group of5w:Point A:34.4±4.8℃,39.0±5.3℃,42.5±5.6℃,45.6±5.6℃,48.1±6.1℃,50.1±6.7℃,52.0±7.0℃,53.1±7.1℃;Point B:41.9±3.4℃,45.6±7.2℃,52.1±4.4℃,55.7±4.4℃,58.8±4.3℃,61.7±4.6℃,63.7±5.2℃,65.4±5.0℃;Point C:28.4±2.9℃,32.0±3.0℃,35.4±3.2℃,38.3±2.9℃,40.3±3.6℃,42.8±3.5℃,44.6±3.8℃,46.0±3.8℃.Group of10w:Point A:41.6±4.3℃,47.2±3.9℃,52.2±3.4℃,56.5±3.4℃,60.6±3.9℃,64.8±4.1℃,68.3±4.3℃,70.8±4.6℃;Point B:55.0±5.2℃,63.7±5.5℃,71.1±4.7℃,77.6±4.0℃,83.1±4.4℃,87.1±5.1℃,91.2±5.3℃,93.9±5.2℃;Point C:32.0±3.8℃,36.5±3.5℃,40.8±3.9℃,44.9±3.9℃,48.2±4.4℃,51.3±4.9℃,53.9±5.9℃,55.6±6.2℃.Group of20w:Point A:51.6±5.3℃,61.1±6.4℃,68.4±8.7℃,74.0±8.6℃,80.2±7.9℃,85.6±6.9℃,90.4±5.8℃,93.5±5.7℃;Point B:77.5±7.0℃,92.0±9.3℃,102.8±9.4℃,114.7±11.8℃,123.9±12.9℃,134.0±10.9℃,142.3±12.0℃,148.0±12.2℃; Point C:37.3±3.0℃,43.2±3.5℃,48.0±4.0℃,52.0±5.3℃,55.4±6.6℃,58.9±7.3℃,63.0±9.6℃,64.8±10.0℃.We compared the temperature of the three-point measured at the equivalent energy for each experimental group, and we found that B> A>C (P<0.05).And compared the temperature of different output power measuredat the same energy for each measurement point, we found that20w>10w>5w (P<0.05)The temperature measured at the three-point increased gradually with the laser radiation energy accumulating for each experimental group(P<0.05). But for group of5w, there was no significant difference of the temperature measured at the three-point when the total laser energy accumulatd over500J (P>0.05).As the experiments shows, for the temperature measurement point that2mm in side of the optical fiber tip, the highest temperature is only about65℃when the laser irradiated at5w. And when the laser irradiated at10w, the temperature can be heated to60℃-70℃(denaturation threshold for tissue) wen the laser energy accumulated up to200J-300J.But when the laser irradiated at20w, the temperature was already closeto100℃when the laser energy just delivered200J.And our results indicated that the maximum temperature measuredat the point that5mm in side of the optical fiber tip approaches approximately65℃when the laser energy accumulated up to800J irradiated at20w.Conclusions: This study demonstrates that different parameters bring about unequal thermal conductivity on intervertebral disc tissue by Nd:YAG laser irradiation. The temperature measured at the three-point increased gradually with the laser radiation energy accumulating. With equivalent laser energy delivered, the tissue temperature rose up when outputpower increased, and weaken down with the distance away from vaporization center increasing. These data suggest that laser parameters should be carefully controlled according to the height of intervertebral space intreatment of cervical or lumbar disc herniation by PLDD. |
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